1. Field of the Invention
The present invention relates to access nodes accommodating a plurality of access methods.
2. Description of Related Art
Over IP networks, typically, the Internet, data is transmitted in compliance with the Internet Protocol (IP) As a service of allowing users to gain access to such IP network, an Internet service is available. Common carriers offering the Internet service are called Internet Service Providers (ISPs). As means of access from a user to an ISP, a Point to Point Protocol (PPP), which has been standardized as Request for Comments (RFC) 1661 by the Internet Engineering Task Force (IETF), is often used. Moreover, an IP connection service is known as the service of relaying a plurality of access requests from users to an ISP. Common carriers offering the IP connection service are called carriers or access providers and they may connect and allocate PPP-compliant access requests from users to an ISP by tunneling. A typical tunneling protocol example is Layer 2 Tunneling Protocol (L2TP) specified in RFC2661.
FIG. 20 shows a illustrative topology organized with networks for implementing a high-speed IP connection service, the conventional high-speed IP connection service in an access method using Digital Subscriber Lines (DSLs), which are typically Asymmetric Digital Subscriber Line (ADSL). The kernel of the high-speed IP connection network comprises broadband access servers BSs that accept access requests from users, BSs that distribute the access requests to ISP networks, an access control server AC12 for controlling access, and a core network CN1, at the entrance of which the former BSs are located and at the exit of which the latter BSs are located. To this kernel, terminals and hosts such as servers are connected. The core network comprises transmission paths and IP routers. Now, take note of a broadband access server BS11. Upon receiving a PPP connection request transferred across a DSL network MN11 which is an access media network and a DSL Access Multiplexer (DSLAM) DL11 from a user IP terminal IT20, the server BS11 queries the access control server AC12 about routing the request and routes it to an ISP network PN11. If there does not exist an L2TP tunnel TL22 for relaying the request to a broadband access server BS13 connecting to the PN11, the broadband access server BS11 issues a request to set up this tunnel. The BS13 queries an access control server AC13 for the PN11 about whether the user who issued the PPP connection request is an authorized user under contract. If the user authentication is verified, an L2TP session is set up between the BS11 and BS13 across the TL22. PPP session PS10 is established in this way as indicated by a bold broken line from the IT20 to the BS13, and the IT20 is then connected to the Internet over the PN11 in the high-speed IP connection mode. In FIG. 20, over the section from the BS13 to the Internet, distinguished by a finer broken line, PPP is no longer used and IP transmission is performed. In FIG. 20, the access control servers AC12 and AC13 are also called Radius servers. In the case of L2TP, the control of the AC12 may be called primary authentication and the control of the AC13 secondary authentication. The BS12 and BS13 are called Broad Access Servers (BASs). In the case of L2TP, functionally, the BS 11 is called an L2TP Access Concentrator (LAC) and the BS 12 an L2TP Network Server (LNS).
FIG. 21 shows an illustrative topology organized with networks for implementing a relatively low-speed IP connection service, the conventional relatively low-speed IP connection service in an access method using telephone networks. Unlike the high-speed IP connection service, in the relatively low-speed IP connection service mode, a terminal IT 22 initially attempts a call for connection request by dial-up. When a switch SW 11 receives the attempted call transmitted over the telephone network MN11 which is an access media network, it transfers the call to an access control server AC11 across a telephone control network MNW10 and the server AC11 activates the access server AS11. Then, after the AS11 receives a PPP connection request form the IT22, routing the request is performed by following the same procedure described for FIG. 20, and eventually an L2TP tunnel TL26 and a PPP session PS11 are set up. Then, the IT22 is connected to the Internet via the PN11 in the relatively low-speed IP connection mode. As the telephone control network MN10 in FIG. 21, a common channel signaling network such as SS7 is often used. The access control server AC11 is also called a Signaling Gateway. The access servers AS11 and AS13 are also called Remote Access Servers (RASs) and functionally the AS11 is called the LAC and the AS13 is called the LNS.
FIG. 22 shows a illustrative topology organized with networks for implementing a mobile network IP connection service, the conventional mobile network IP connection service in an access method using a mobile network such as radio channels. Unlike the high-speed or relatively low-speed IP connection service, in the mobile IP connection service mode, a mobile node MoN11 initially receives a connection request from a terminal IT 24 transmitted over a mobile network MN13 which is an access media network. A tunnel TL 34 from the MoN11 to a mobile access node MA11 is set up by using Generic Routing Encapsulation (GRE) or the like. After that, routing the request is performed by following the same procedure described for FIG. 20 and eventually an L2TP tunnel or Mobile IP tunnel 31 and a PPP session PS12 are set up. Then, the IT24 is connected to the Internet over the PN11 in the mobile network IP connection mode. As the IT 24 moves, the tunnel between the MA11 and MA13 is removed and another tunnel is set up accordingly so that offering of the IP connection service continues even if the user moves. Diverse types of the mobile network MN 13 shown in FIG. 22 are available; e.g., General Packet Radio Service (GPRS) network, IMT2000 network, High Data Rate (HDR) network, etc. Diverse types of the mobile node MoN11 are available; e.g., Packet Control Function (PCF), Access Point (AP), etc. Diverse types of the mobile access node MA13 are available; e.g., Home Agent (HA), Gateway GPRS Support Node (GGSN), etc.
FIG. 23 shows an illustrative hardware configuration of a conventional high-speed IP router. The high-speed IP router, shown in FIG. 23, has line interface units and IP processing units on the input and output sides and a switch unit connects both sides. Its control unit has control over the router and its components. Because the IP processing units perform high-speed processing only for forwarding packets in compliance with the IP protocol, using ASIC or the like, generally, the router is not engaged in the above-described session and tunnel setup based on PPP, L2TP, etc. required for IP connection services.
FIG. 24 shows an illustrative hardware configuration of a conventional PAS. The RAS, shown in FIG. 24, has line interface units and modem and HDLC processing units on the input and output sides and a bus or switch unit connect both sides. Its control unit has control over the RAS and its components and moreover, it is engaged in IP processing and session setup based on PPP, L2TP, etc., thus implementing the RAS function.
As described above, separate communications equipments have so far been required for different access methods; i.e., high-speed access servers for the network implementing the high-speed IP connection service, access servers for the network implementing the relatively low-speed IP connection service, and mobile access nodes for the network implementing the mobile network IP connection service. For example, if a common carrier that now offers the relatively low-speed IP connection service plans to offer the high-speed IP connection service, it has to procure new equipment of another type which costs a lot. Adding another type of equipment complicates the management. Such a problem was posed that the investment in the facilities would become vain if most users shifted from the relatively low-speed IP connection service to the high-speed IP connection service. The same is true for when the common carrier plans to offer the mobile network IP connection service in addition to the existing services. Partly due to that, inevitably, some carriers offer fixed network services only whereas other carriers offer mobile network services only.
To make an access server or node accommodate the plurality of access methods, a conceivable method is changing the software to run on the IP router that carries out software-controlled packet switching. However, the IP router for IP packet switching configured in hardware has lately been used to implement high-speed data packet transmission. The performance of the software-controlled IP packet switching is significantly lower than the performance of the high-speed IP router configured in hardware. Thus, the software-controlled processing does not serve practical high-speed packet switching needs, though it maybe acceptable for the RAS that carries out only the relatively low-speed IP connection. Another problem is that the RAS generally has STM line interfaces dedicated to the access over a telephone network and connection ports for connecting to an access control server and its structure is different from other access servers or nodes.